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Sep 19, 2013
09/13

by
Henning Schomerus

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In semiclassical studies of systems with mixed phase space, the neighbourhood of bifurcations of co-dimension two is felt strongly even though such bifurcations are ungeneric in classical mechanics. We discuss a scenario which reveals this fact and derive the correct semiclassical contribution of the bifurcating orbits to the trace of the unitary time evolution operator. That contribution has a certain collective character rather than being additive in the individual periodic orbits involved....

Source: http://arxiv.org/abs/chao-dyn/9703003v1

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Sep 20, 2013
09/13

by
Henning Schomerus

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I review how methods from mesoscopic physics can be applied to describe the multiple wave scattering and complex wave dynamics in non-hermitian PT-symmetric resonators, where an absorbing region is coupled symmetrically to an amplifying region. Scattering theory serves as a convenient tool to classify the symmetries beyond the single-channel case and leads to effective descriptions which can be formulated in the energy domain (via Hamiltonians) and in the time domain (via time evolution...

Source: http://arxiv.org/abs/1207.1454v2

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Sep 22, 2013
09/13

by
Henning Schomerus

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The observation that PT-symmetric Hamiltonians can have real-valued energy levels even if they are non-Hermitian has triggered intense activities, with experiments, in particular, focusing on optical systems, where Hermiticity can be broken by absorption and amplification. For classical waves, absorption and amplification are related by time-reversal symmetry. This work shows that microreversibility-breaking quantum noise turns PT-symmetric systems into self-sustained sources of radiation,...

Source: http://arxiv.org/abs/1001.0539v2

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Sep 18, 2013
09/13

by
Volker Schomerus

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In this work we propose an exact solution of the c=1 Liouville model, i.e. of the world-sheet theory that describes the homogeneous decay of a closed string tachyon. Our expressions are obtained through careful extrapolation from the correlators of Liouville theory with c > 25. In the c=1 limit, we find two different theories which differ by the signature of Liouville field. The Euclidean limit coincides with the interacting c=1 theory that was constructed by Runkel and Watts as a limit of...

Source: http://arxiv.org/abs/hep-th/0306026v1

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Sep 21, 2013
09/13

by
Henning Schomerus

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We investigate classical and semiclassical aspects of codimension--two bifurcations of periodic orbits in Hamiltonian systems. A classification of these bifurcations in autonomous systems with two degrees of freedom or time-periodic systems with one degree of freedom is presented. We derive uniform approximations to be used in semiclassical trace formulas and determine also certain global bifurcations in conjunction with Stokes transitions that become important in the ensuing diffraction...

Source: http://arxiv.org/abs/chao-dyn/9711013v1

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Jul 20, 2013
07/13

by
Henning Schomerus

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We describe an angularly asymmetric interface-scattering mechanism which allows to spatially separate the electrons in the two low-energy valleys of bilayer graphene. The effect occurs at electrostatically defined interfaces separating regions of different pseudospin polarization, and is associated with the helical winding of the pseudospin vector across the interface, which breaks the reflection symmetry in each valley. Electrons are transmitted with a preferred direction of up to 60 degree...

Source: http://arxiv.org/abs/1007.4594v2

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Sep 21, 2013
09/13

by
Henning Schomerus

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One of the principal goals in the design of photonic crystals is the engineering of band gaps and defect states. Drawing on the concepts of band-structure topology, I here describe the formation of exponentially localized, topologically protected midgap states in photonic systems with spatially distributed gain and loss. When gain and loss are suitably arranged these states maintain their topological protection and then acquire a selectively tunable amplification rate. This finds applications...

Source: http://arxiv.org/abs/1301.0777v1

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Jul 19, 2013
07/13

by
Volker Schomerus

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It has been discussed earlier that ( weak quasi-) quantum groups allow for conventional interpretation as internal symmetries in local quantum theory. From general arguments and explicit examples their consistency with (braid-) statistics and locality was established. This work addresses to the reconstruction of quantum symmetries and algebras of field operators. For every algebra $\A$ of observables satisfying certain standard assumptions, an appropriate quantum symmetry is found. Field...

Source: http://arxiv.org/abs/hep-th/9401042v1

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Sep 18, 2013
09/13

by
Henning Schomerus

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Recent investigations address transport through ballistic charge-neutral graphene strips coupled to doped graphitic leads. This paper shows that identical transport properties arise when the leads are replaced by quantum wires. This duality between graphitic and metallic leads originates in the selection of modes with transverse momentum close to the K points, and can be extended to a wide class of contact models. Among this class we identify a simple, effective contact model, which provides an...

Source: http://arxiv.org/abs/cond-mat/0611209v2

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Sep 18, 2013
09/13

by
Volker Schomerus

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In this note we explain how world-volume geometries of D-branes can be reconstructed within the microscopic framework where D-branes are described through boundary conformal field theory. We extract the (non-commutative) world-volume algebras from the operator product expansions of open string vertex operators. For branes in a flat background with constant non-vanishing B-field, the operator products are computed perturbatively to all orders in the field strength. The resulting series coincides...

Source: http://arxiv.org/abs/hep-th/9903205v1

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Sep 18, 2013
09/13

by
Volker Schomerus

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This is an introduction to the microscopic techniques of non-rational bulk and boundary conformal field theory which are needed to describe strings moving in non-compact curved backgrounds. The latter arise e.g. in the context of AdS/CFT-like dualities and for studies of time-dependent processes. After a general outline of the central concepts, we focus on two specific but rather prototypical models: Liouville field theory and the 2D cigar. Rather than following the historical path, the...

Source: http://arxiv.org/abs/hep-th/0509155v1

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Aug 6, 2017
08/17

by
Friedrich Schomerus

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Topic: business management

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Sep 19, 2013
09/13

by
Volker Schomerus

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These lectures provide an introduction to the microscopic description of branes in curved backgrounds. After a brief reminder of the flat space theory, the basic principles and techniques of (rational) boundary conformal field theory are presented in the second lecture. The general formalism is then illustrated through a detailed discussion of branes on compact group manifolds. In the final lecture, many more recent developments are reviewed, including some results for non-compact target spaces.

Source: http://arxiv.org/abs/hep-th/0209241v1

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Sep 20, 2013
09/13

by
Volker Schomerus

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Over the last few years, string theory has changed profoundly. Most importantly, novel duality relations have emerged which involve gauge theories of brane excitations on one side and various closed string backgrounds on the other. In this lecture, we introduce the fundamental ingredients of modern string theory and explain how they are modeled through 2D (boundary) conformal field theory. This so-called `microscopic description' of strings and branes is an active research area with new results...

Source: http://arxiv.org/abs/hep-th/0404262v1

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Sep 24, 2013
09/13

by
H. Schomerus

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We investigate the effects of wave localization on the delay time tau (frequency sensitivity of the scattering phase shift) of a wave transmitted through a disordered wave guide. Localization results in a separation tau=chi+chi' of the delay time into two independent but equivalent contributions, associated to the left and right end of the wave guide. For N=1 propagating modes, chi and chi' are identical to half the reflection delay time of each end of the wave guide. In this case the...

Source: http://arxiv.org/abs/cond-mat/0103113v1

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Jun 29, 2018
06/18

by
Henning Schomerus

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Over the past decades, a great body of theoretical and mathematical work has been devoted to random-matrix descriptions of open quantum systems. In these notes, based on lectures delivered at the Les Houches Summer School "Stochastic Processes and Random Matrices" in July 2015, we review the physical origins and mathematical structures of the underlying models, and collect key predictions which give insight into the typical system behaviour. In particular, we aim to give an idea how...

Topics: Disordered Systems and Neural Networks, Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1610.05816

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Sep 21, 2013
09/13

by
Volker Schomerus

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During the last ten years, intriguing dualities between gauge and string theory have been found and explored. They provide a novel window on strongly coupled gauge physics, including QCD-like models. Based on a short historical review of modern string theory, we shall explain how so-called AdS/CFT dualities emerged at the end of the 1990s. Some of their concrete implications and remarkable recent progress are then illustrated for the simplest example, namely the multicolor limit of \N=4 Super...

Source: http://arxiv.org/abs/0706.1209v1

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Sep 21, 2013
09/13

by
Henning Schomerus

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PT-symmetric systems can have a real spectrum even when their Hamiltonian is non-hermitian, but develop a complex spectrum when the degree of non-hermiticity increases. Here we utilize random-matrix theory to show that this spontaneous PT-symmetry breaking can occur via two distinct mechanisms, whose predominance is associated to different universality classes. Present optical experiments fall into the orthogonal class, where symmetry-induced level crossings render the characteristic absorption...

Source: http://arxiv.org/abs/1011.1385v1

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Sep 23, 2013
09/13

by
Henning Schomerus

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We investigate broken rational tori consisting of a chain of four (rather than two) periodic orbits. The normal form that describes this configuration is identified and used to construct a uniform semiclassical approximation, which can be utilized to improve trace formulae. An accuracy gain can be achieved even for the situation when two of the four orbits are ghosts. This is illustrated for a model system, the kicked top.

Source: http://arxiv.org/abs/chao-dyn/9904003v1

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Sep 18, 2013
09/13

by
Henning Schomerus

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A recent paper [Jokela et al, arxiv:0806.1491 9 June 2008] contains a surmise about an expectation value in a Coulomb gas which interacts with an additional charge xi that sits at a fixed position. Here I demonstrate the validity of the surmised expression and extend it to a certain class of higher cumulants. The calculation is based on the analogy to statistical averages in the circular unitary ensemble of random-matrix theory and exploits properties of orthogonal polynomials on the unit...

Source: http://arxiv.org/abs/0806.2602v3

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Sep 18, 2013
09/13

by
Henning Schomerus

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This work presents a theory of the frequency-resolved light emission of active two-dimensional dielectric microresonators, which are characterized by a highly non-paraxial mode structure and frequently feature a position-dependent dielectric constant and non-uniform gain. The Lorentzian intensity profile is characterized by an appropriately generalized Petermann factor, a renormalized peak position, and the cold-cavity resonance lifetime Gamma. The theory also delivers a relation of Gamma to...

Source: http://arxiv.org/abs/0809.2349v2

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Sep 18, 2013
09/13

by
Henning Schomerus; Eric Lutz

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We investigate decoherence in the quantum kicked rotator (modelling cold atoms in a pulsed optical field) subjected to noise with power-law tail waiting-time distributions of variable exponent (Levy noise). We demonstrate the existence of a regime of nonexponential decoherence where the notion of a decoherence rate is ill-defined. In this regime, dynamical localization is never fully destroyed, indicating that the dynamics of the quantum system never reaches the classical limit. We show that...

Source: http://arxiv.org/abs/quant-ph/0611162v1

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Sep 22, 2013
09/13

by
Sylvain Ribault; Volker Schomerus

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We present a comprehensive analysis of branes in the Euclidean 2D black hole (cigar). In particular, exact boundary states and annulus amplitudes are provided for D0-branes which are localized at the tip of the cigar as well as for two families of extended D1 and D2-branes. Our results are based on closely related studies for the Euclidean AdS3 model and, as predicted by the conjectured duality between the 2D black hole and the sine-Liouville model, they share many features with branes in...

Source: http://arxiv.org/abs/hep-th/0310024v3

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Sep 19, 2013
09/13

by
Henning Schomerus; Fritz Haake

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We determine semiclassical quasienergy spectra from periodic orbits for a system with a mixed phase space, the kicked top. Throughout the transition from integrability to well developed chaos the standard error incurred for the quasienergies is a small percentage of their mean spacing. Such fine accuracy does not even require the angular momentum quantum number $j\propto 1/\hbar$ to be large; it already prevails for $j=1,2,3$. To open the way towards a reliable spectrum the conventional trace...

Source: http://arxiv.org/abs/chao-dyn/9703016v1

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Jul 20, 2013
07/13

by
Henning Schomerus; Jakub Tworzydlo

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In the semiclassical limit of open ballistic quantum systems, we demonstrate the emergence of instantaneous decay modes guided by classical escape faster than the Ehrenfest time. The decay time of the associated quasi-bound states is smaller than the classical time of flight. The remaining long-lived quasi-bound states obey random-matrix statistics, renormalized in compliance with the recently proposed fractal Weyl law for open systems [W. T. Lu, S. Sridhar, and M. Zworski, Phys. Rev. Lett. 91,...

Source: http://arxiv.org/abs/cond-mat/0406135v2

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Sep 18, 2013
09/13

by
Stefan Fredenhagen; Volker Schomerus

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In this work we study the dynamics of branes on group manifolds G deep in the stringy regime. After giving a brief overview of the various branes that can be constructed within the boundary conformal field theory approach, we analyze in detail the condensation processes that occur on stacks of such branes. At large volume our discussion is based on certain effective gauge theories on non-commutative `fuzzy' spaces. Using the `absorption of the boundary spin'-principle which was formulated by...

Source: http://arxiv.org/abs/hep-th/0012164v1

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Sep 22, 2013
09/13

by
S. Fredenhagen; V. Schomerus

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We propose a new rule for boundary renormalization group flows in fixed-point free coset models. Our proposal generalizes the 'absorption of boundary spin'-principle formulated by Affleck and Ludwig to a large class of perturbations in boundary conformal field theories. We illustrate the rule in the case of unitary minimal models.

Source: http://arxiv.org/abs/hep-th/0205011v1

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Sep 21, 2013
09/13

by
G. Mack; V. Schomerus

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Quantum field planes furnish a noncommutative differential algebra $\Omega$ which substitutes for the commutative algebra of functions and forms on a contractible manifold. The data required in their construction come from a quantum field theory. The basic idea is to replace the ground field ${\bf C}$ of quantum planes by the noncommutative algebra ${\cal A}$ of observables of the quantum field theory.

Source: http://arxiv.org/abs/hep-th/9403170v1

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Sep 17, 2013
09/13

by
Yasuaki Hikida; Volker Schomerus

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We propose exact formulas for the 2- and 3-point functions of the WZNW model on the non-compact supergroup OSP(1|2). Using the path integral approach that was recently developed in arXiv:0706.1030 we show how local correlation functions in the OSP(p|2) WZNW models can be obtained from those of N=p supersymmetric Liouville field theory for p=1,2. We then employ known results on correlators in N=1 Liouville theory to determine the structure constants of the OSP(1|2) theory.

Source: http://arxiv.org/abs/0711.0338v2

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Sep 21, 2013
09/13

by
Stefan Fredenhagen; Volker Schomerus

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In this note we discuss bound states of un- or meta-stable brane configurations in various non-trivial (curved) backgrounds. We begin by reviewing some known results concerning brane dynamics on group manifolds. These are then employed to study condensation in cosets of the WZW model. While the basic ideas are more general, our presentation focuses on parafermion theories and, closely related, N=2 superconformal minimal models. We determine the (non-commutative) low energy effective actions for...

Source: http://arxiv.org/abs/hep-th/0104043v1

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Sep 17, 2013
09/13

by
Anton Alekseev; Volker Schomerus

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We consider the contribution of the B-field into the RR charge of a spherical D2-brane. Extending a recent analysis of Taylor, we show that the boundary and bulk contributions do not cancel in general. Instead, they add up to an integer as observed by Stanciu. The general formula is applied to compute the RR charges of spherical D-branes of the SU(2) WZW model at level k and it shows that these RR charges are only defined modulo k+2. We support this claim by studying bound state formation of...

Source: http://arxiv.org/abs/hep-th/0007096v1

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Sep 19, 2013
09/13

by
H. Schomerus; M. Titov

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We analyze the conductance distribution function in the one-dimensional Anderson model of localization, for arbitrary energy. For energy at the band center the distribution function deviates from the universal form assumed in single-parameter scaling theory. A direct link to the break-down of the random-phase approximation is established. Our findings are confirmed by a parameter-free comparison to the results of numerical simulations.

Source: http://arxiv.org/abs/cond-mat/0208457v1

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Sep 22, 2013
09/13

by
M. Hentschel; H. Schomerus

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We discuss curvature corrections to Fresnel's laws for the reflection and transmission of light at a non-planar refractive-index boundary. The reflection coefficients are obtained from the resonances of a dielectric disk within a sequential-reflection model. The Goos-H\"anchen effect for curved light fronts at a planar interface can be adapted to provide a qualitative and quantitative extension of the ray model which explains the observed deviations from Fresnel's laws.

Source: http://arxiv.org/abs/physics/0111160v1

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Sep 22, 2013
09/13

by
Stefan Fredenhagen; Volker Schomerus

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The analysis of D-branes in coset models G/H provides a natural extension of recent studies on branes in WZW-theory and it has various interesting applications to physically relevant models. In this work we develop a reduction procedure that allows to construct the non-commutative gauge theories which govern the dynamics of branes in G/H. We obtain a large class of solutions and interprete the associated condensation processes geometrically. The latter are used to propose conservation laws for...

Source: http://arxiv.org/abs/hep-th/0111189v2

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Sep 22, 2013
09/13

by
M. Kopp; H. Schomerus

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Weyl's law approximates the number of states in a quantum system by partitioning the energetically accessible phase-space volume into Planck cells. Here we show that typical resonances in generic open quantum systems follow a modified, fractal Weyl law, even though their classical dynamics is not globally chaotic but also contains domains of regular motion. Besides the obvious ramifications for quantum decay, this delivers detailed insight into quantum-to-classical correspondence, a phenomenon...

Source: http://arxiv.org/abs/0906.5320v1

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Jun 29, 2018
06/18

by
Mikhail Isachenkov; Volker Schomerus

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We observe that conformal blocks of scalar 4-point functions in a $d$-dimensional conformal field theory can mapped to eigenfunctions of a 2-particle hyperbolic Calogero-Sutherland Hamiltonian. The latter describes two coupled P\"oschl-Teller particles. Their interaction, whose strength depends smoothly on the dimension $d$, is known to be superintegrable. Our observation enables us to exploit the rich mathematical literature on Calogero-Sutherland models in deriving various results for...

Topic: High Energy Physics - Theory

Source: http://arxiv.org/abs/1602.01858

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Jun 28, 2018
06/18

by
Arthur Lipstein; Volker Schomerus

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In this note we address the worldsheet description of 4-dimensional N=8 supergravity using ambitwistors. After gauging an appropriate current algebra, we argue that the only physical vertex operators correspond to the N=8 supermultiplet. It has previously been shown that worldsheet correlators give rise to supergravity tree level scattering amplitudes. We extend this work by proposing a definition for genus-one amplitudes that passes several consistency checks such as exhibiting modular...

Topic: High Energy Physics - Theory

Source: http://arxiv.org/abs/1507.02936

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Sep 22, 2013
09/13

by
Stefan Fredenhagen; Volker Schomerus

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In this note we reconsider the minisuperspace toy models for rolling and bouncing tachyons. We show that the theories require to choose boundary conditions at infinity since particles in an exponentially unbounded potential fall to infinity in finite world-sheet time. Using standard techniques from operator theory, we determine the possible boundary conditions and we compute the corresponding energy spectra and minisuperspace 3-point functions. Based on this analysis we argue in particular that...

Source: http://arxiv.org/abs/hep-th/0308205v1

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Sep 22, 2013
09/13

by
Christopher Birchall; Henning Schomerus

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We consider the transport of electrons passing through a mesoscopic device possessing internal dynamical quantum degrees of freedom. The mutual interaction between the system and the conduction electrons contributes to the current fluctuations, which we describe in terms of full counting statistics. We identify conditions where this discriminates coherent from incoherent internal dynamics, and also identify and illustrate conditions under which the device acts to dynamically bunch transmitted...

Source: http://arxiv.org/abs/1004.5298v1

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Sep 18, 2013
09/13

by
Andor Kormanyos; Henning Schomerus

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When a quantum-chaotic normal conductor is coupled to a superconductor, random-matrix theory predicts that a gap opens up in the excitation spectrum which is of universal size $E_g^{\rm RMT}\approx 0.3 \hbar/t_D$, where $t_D$ is the mean scattering time between Andreev reflections. We show that a scarred state of long lifetime $t_S\gg t_D$ suppresses the excitation gap over a window $\Delta E\approx 2 E_g^{\rm RMT}$ which can be much larger than the narrow resonance width $\Gamma_S=\hbar/t_S$...

Source: http://arxiv.org/abs/cond-mat/0605205v1

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Sep 19, 2013
09/13

by
H. Schomerus; M. Titov

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We investigate the short-distance statistics of the local density of states nu in long one-dimensional disordered systems, which display Anderson localization. It is shown that the probability distribution function P(nu) can be recovered from the long-distance wavefunction statistics, if one also uses parameters that are irrelevant from the perspective of two-parameter scaling theory.

Source: http://arxiv.org/abs/cond-mat/0302148v2

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Sep 18, 2013
09/13

by
Thomas Quella; Volker Schomerus

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The aim of this work is to present a general theory of coset models G/H in which different left and right actions of H on G are gauged. Our main results include a formula for their modular invariant partition function, the construction of a large set of boundary states and a general description of the corresponding brane geometries. The paper concludes with some explicit applications to the base of the conifold and to the time-dependent Nappi-Witten background.

Source: http://arxiv.org/abs/hep-th/0212119v3

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Sep 21, 2013
09/13

by
Yasuaki Hikida; Volker Schomerus

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There exists an intriguing relation between genus zero correlation functions in the H^+_3 WZNW model and in Liouville field theory. We provide a path integral derivation of the correspondence and then use our new approach to generalize the relation to surfaces of arbitrary genus g. In particular we determine the correlation functions of N primary fields in the WZNW model explicitly through Liouville correlators with N+2g-2 additional insertions of certain degenerate fields. The paper concludes...

Source: http://arxiv.org/abs/0706.1030v3

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Sep 22, 2013
09/13

by
Volker Schomerus; Paulina Suchanek

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N=1 super Liouville field theory is one of the simplest non-rational conformal field theories. It possesses various important extensions and interesting applications, e.g. to the AGT relation with 4D gauge theory or the construction of the OSP(1|2) WZW model. In both setups, the N=1 Liouville field is accompanied by an additional free fermion. Recently, Belavin et al. suggested a bosonization of the product theory in terms of two bosonic Liouville fields. While one of these Liouville fields is...

Source: http://arxiv.org/abs/1210.1856v1

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Sep 18, 2013
09/13

by
Andreas Recknagel; Volker Schomerus

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D-branes in curved backgrounds can be treated with techniques of boundary conformal field theory. We discuss the influence of scalar condensates on such branes, i.e. perturbations of boundary conditions by marginal boundary operators. A general criterion is presented that guarantees a boundary perturbation to be truly marginal in all orders of perturbation theory. Our results on boundary deformations have several interesting applications which are sketched at the end of this note.

Source: http://arxiv.org/abs/hep-th/9903139v1

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Sep 22, 2013
09/13

by
P. Samuelsson; H. Schomerus

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We present a theory for the nonequilibrium current in a mesoscopic Josephson junction which is coupled to a normal electron reservoir, and apply it to a chaotic junction. Large sample-to-sample fluctuations of the critical current $I_{\rm c}$ are found, with ${rms} I_{\rm c} \simeq \sqrt{N}e\Delta/\hbar$, when the voltage difference eV between the electron reservoir and the junction exceeds the superconducting gap $\Delta$ and the number of modes N connecting the junction to the superconducting...

Source: http://arxiv.org/abs/cond-mat/0004197v1

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Sep 22, 2013
09/13

by
Yasuaki Hikida; Volker Schomerus

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We prove that the cigar conformal field theory is dual to the Sine-Liouville model, as conjectured originally by Fateev, Zamolodchikov and Zamolodchikov. Since both models possess the same chiral algebra, our task is to show that correlations of all tachyon vertex operators agree. We accomplish this goal through an off-critical version of the geometric Langlands duality for sl(2). More explicitly, we combine the well-known self-duality of Liouville theory with an intriguing correspondence...

Source: http://arxiv.org/abs/0805.3931v1

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Sep 21, 2013
09/13

by
Constantin Candu; Volker Schomerus

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We describe several families of non-unitary coset conformal field theories that possess truly marginal couplings. These generalize the known examples of Wess-Zumino-Witten models on supergroups such as PSU(n|n) or OSP(2n+2|2n). Our extension includes coset space sigma models, affine Toda theories or Gross-Neveu models which are believed to arise in certain limits.

Source: http://arxiv.org/abs/1104.5028v1

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Sep 19, 2013
09/13

by
M. Titov; H. Schomerus

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We study analytically the local density of states in a disordered normal-metal wire at ballistic distance to a superconductor. Our calculation is based on a scattering-matrix approach, which concerns for wave-function localisation in the normal metal, and extends beyond the conventional semiclassical theory based on Usadel and Eilenberger equations. We also analyse how a finite transparency of the NS interface modifies the spectral proximity effect and demonstrate that our results agree in the...

Source: http://arxiv.org/abs/cond-mat/0208107v2